Normalization of sector amplitudes using monopole amplitudes
A method and apparatus for normalizing an acoustic wellbore tool by correcting measured sector acoustic signals due to changes in pressure and temperature downhole, the method and apparatus comprising an acoustic wellbore tool having at least one monopole transmitter and monopole receiver, and one or more sector transmitters and receivers disposed along the longitudinal axis of the tool, determining the attenuation values of received monopole and sector acoustic signals, determining a correction ratio using an average sector attenuation value and a theoretical attenuation value, and correcting the sector acoustic signals using the correction ratio.
1. A method for normalizing signals of an acoustic wellbore tool having at least one monopole transmitter and at least one monopole receiver disposed along a longitudinal axis of the tool and having one or more sector transmitters and one or more sector receivers disposed along the longitudinal axis of the tool, the method comprising:
firing the at least one monopole transmitter and recording at least one monopole acoustic signal received at the at least one monopole receiver;
determining at least one theoretical attenuation value of the at least one monopole acoustic signal;
firing the one or more sector transmitters and recording one or more sector acoustic signals received at the one or more sector receivers;
determining one or more sector attenuation values of the one or more sector acoustic signals;
determining a sector correction ratio using an average of the one or more sector attenuation values and using the at least one theoretical attenuation value; and
applying the sector correction ratio to the one or more sector acoustic signals to determine corrected amplitude values of the one or more sector acoustic signals.
2. The method of claim 1 , wherein the at least one theoretical attenuation value represents the attenuation value of the at least one monopole acoustic signal received by the at least one monopole receiver having a longitudinal displacement from the at least one monopole transmitter equal to the longitudinal displacement of the one or more sector receivers from the respective one or more sector transmitters.
3. The method of claim 1 , wherein the at least one theoretical attenuation value of the at least one monopole acoustic signal is determined using the equation:
Monopole
Attn
Value
=
(
K
)
(
20
)
Log
10
(
Raw
Amp
Max
Amp
)
where
Raw Amp is the amplitude value of the at least one monopole acoustic signal,
K is a constant determined as a function of transmitter-receiver spacing and operating frequency,
Max Amp is the overall maximum measured amplitude value of the monopole acoustic signal as the measured monopole acoustic signal amplitude values vary with changes in pressure in the wellbore, and
Monopole Attn Value is the attenuation value of the at least one monopole acoustic signal.
4. The method of claim 1 , wherein the one or more sector attenuation values of the one or more sector acoustic signals are determined using the equation:
Sector
Attn
Value
(
n
)
=
(
K
)
(
20
)
Log
10
(
Raw
Amp
(
n
)
Max
Amp
(
n
)
)
where
(n) comprises the one or more sector acoustic signals,
K is a constant determined as a function of transmitter-receiver spacing and operating frequency,
Raw Amp (n) comprises the amplitude value of the (n)th sector acoustic signal,
Max Amp (n) comprises the overall maximum measured amplitude value of the (n)th sector acoustic signal as the measured amplitude value of the (n)th sector acoustic signal varies with changes in pressure in the wellbore, and
Sector Attn Value (n) comprises the attenuation value of the (n)th sector acoustic signal.
5. The method of claim 1 , wherein the at least one theoretical attenuation value of the at least one monopole acoustic signal is determined using the equation:
Theoretical Attn Value=( K )(Monopole Attn Value)
where
Monopole Attn Value comprises the attenuation value of the at least one monopole acoustic signal,
K is a constant determined as a function of transmitter-receiver spacing and operating frequency, and
Theoretical Attn Value comprises the theoretical attenuation value for the at least one monopole acoustic signal.
6. The method of claim 1 , wherein the correction ratio is determined using the equation:
Correction
Ratio
=
(
Theoretical
Attn
Value
Avg
Sector
Attn
)
where
Correction Ratio comprises the correction ratio,
Theoretical Attn Value comprises the theoretical attenuation value of the at least one monopole acoustic signal, and
Avg Sector Attn is the average sector attenuation value of the one or more sector attenuation values for the one or more sector acoustic signals.
7. The method of claim 6 , wherein the Avg Sector Attn is determined by adding the one or more sector attenuation values of the one or more sector acoustic signals and dividing the sum by the number of the one or more sector acoustic signals.
8. The method of claim 1 , wherein to determine the corrected amplitude values of the one or more sector acoustic signals, the method comprises determining corrected attenuation values of the one or more sector acoustic signals by the equation:
Corrected Attn Value ( n )=Correction Ratio*Sector Attn Value ( n )
where
(n) comprises the one or more sector acoustic signals,
Corrected Attn Value (n) comprises the corrected attenuation value of the (n)th sector acoustic signal, and
Sector Attn Value (n) comprises the sector attenuation value of the (n)th sector acoustic signal.
9. The method of claim 1 , wherein the longitudinal displacement between the at least one monopole transmitter and the at least one monopole receiver is greater than the longitudinal displacement between the one or more sector transmitters and the respective one or more sector receivers.
10. The method of claim 1 , wherein determining the corrected amplitude values of the one or more sector acoustic signals using the corrected attenuation values of the one or more sector acoustic signals is determined by the equation:
Correction
Sector
Amp
(
n
)
=
10
^
(
Corrected
Attn
Value
(
n
)
10
)
*
Max
Amp
(
n
)
where
(n) comprises the one or more sector acoustic signals,
Corrected Attn Value (n) comprises the corrected attenuation value of the (n)th sector acoustic signal, and
Max Amp (n) comprises the overall maximum measured amplitude value of the (n)th sector acoustic signal as the measured amplitude value of the (n)th sector acoustic signal varies with changes in pressure in the wellbore.
11. A logging tool, comprising:
at least one monopole transmitter and at least one monopole receiver disposed along a longitudinal axis of the logging tool;
one or more sector transmitters and one or more sector receivers disposed along the longitudinal axis of the logging tool;
at least one processor communicatively coupled to the at least one monopole transmitter, the at least one monopole receiver, the one or more sector transmitters and the one or more sector receivers;
memory communicatively coupled to the at least one processor and storing instructions thereon to cause the one or more processors to:
fire the at least one monopole transmitter and record at least one monopole acoustic signal received at the at least one monopole receiver;
determine at least one theoretical attenuation value of the at least one monopole acoustic signal;
fire the one or more sector transmitters and record one or more sector acoustic signals received at the one or more sector receivers;
determine one or more sector attenuation values of the one or more sector acoustic signals;
determine a sector correction ratio using an average of the one or more sector attenuation values and using the at least one theoretical attenuation value; and
apply the sector correction ratio to the one or more sector acoustic signals to determine corrected amplitude values of the one or more sector acoustic signals.
12. The logging tool of claim 11 , wherein the at least one theoretical attenuation value represents the attenuation value of the at least one monopole acoustic signal received by the at least one monopole receiver having a longitudinal displacement from the at least one monopole transmitter equal to the longitudinal displacement of the one or more sector receivers from the respective one or more sector transmitters.
13. The logging tool of claim 11 , wherein the at least one theoretical attenuation value of the at least one monopole acoustic signal is determined using the equation:
Monopole
Attn
Value
=
(
K
)
(
20
)
Log
10
(
Raw
Amp
Max
Amp
)
where
Raw Amp is the amplitude value of the at least one monopole acoustic signal,
K is a constant determined as a function of transmitter-receiver spacing and operating frequency,
Max Amp is the overall maximum measured amplitude value of the monopole acoustic signal as the measured monopole acoustic signal amplitude values vary with changes in pressure in the wellbore, and
Monopole Attn Value is the attenuation value of the at least one monopole acoustic signal.
14. The logging tool of claim 11 , wherein the one or more sector attenuation values of the one or more sector acoustic signals are determined using the equation:
Sector
Attn
Value
(
n
)
=
(
K
)
(
20
)
Log
10
(
Raw
Amp
(
n
)
Max
Amp
(
n
)
)
where
(n) comprises the one or more sector acoustic signals,
K is a constant determined as a function of transmitter-receiver spacing and operating frequency,
Raw Amp (n) comprises the amplitude value of the (n)th sector acoustic signal,
Max Amp (n) comprises the overall maximum measured amplitude value of the (n)th sector acoustic signal as the measured amplitude value of the (n)th sector acoustic signal varies with changes in pressure in the wellbore, and
Sector Attn Value (n) comprises the attenuation value of the (n)th sector acoustic signal.
15. The logging tool of claim 11 , wherein the at least one theoretical attenuation value of the at least one monopole acoustic signal is determined using the equation:
Theoretical Attn Value=( K )(Monopole Attn Value)
where
Monopole Attn Value comprises the attenuation value of the at least one monopole acoustic signal,
K is a constant determined as a function of transmitter-receiver spacing and operating frequency, and
Theoretical Attn Value comprises the theoretical attenuation value for the at least one monopole acoustic signal.
16. The logging tool of claim 11 , wherein the correction ratio is determined using the equation:
Correction
Ratio
=
(
Theoretical
Attn
Value
Avg
Sector
Attn
)
where
Correction Ratio comprises the correction ratio,
Theoretical Attn Value comprises the theoretical attenuation value of the at least one monopole acoustic signal, and
Avg Sector Attn is the average sector attenuation value of the one or more sector attenuation values for the one or more sector acoustic signals.
17. The logging tool of claim 16 , wherein the Avg Sector Attn is determined by adding the one or more sector attenuation values of the one or more sector acoustic signals and dividing the sum by the number of the one or more sector acoustic signals.
18. The logging tool of claim 11 , wherein to determine the corrected amplitude values of the one or more sector acoustic signals, corrected attenuation values of the one or more sector acoustic signals are determined by the equation:
Corrected Attn Value ( n )=Correction Ratio*Sector Attn Value ( n )
where
(n) comprises the one or more sector acoustic signals,
Corrected Attn Value (n) comprises the corrected attenuation value of the (n)th sector acoustic signal, and
Sector Attn Value (n) comprises the sector attenuation value of the (n)th sector acoustic signal.
19. The logging tool of claim 11 , wherein the longitudinal displacement between the at least one monopole transmitter and the at least one monopole receiver is greater than the longitudinal displacement between the one or more sector transmitters and the respective one or more sector receivers.
20. The logging tool of claim 11 , wherein the corrected amplitude values of one or more sector acoustic signals are determined by the equation:
Correction
Sector
Amp
(
n
)
=
10
^
(
Corrected
Attn
Value
(
n
)
10
)
*
Max
Amp
(
n
)
where
(n) comprises the one or more sector acoustic signals,
Corrected Attn Value (n) comprises the corrected attenuation value of the (n)th sector acoustic signal, and
Max Amp (n) comprises the overall maximum measured amplitude value of the (n)th sector acoustic signal as the measured amplitude value of the (n)th sector acoustic signal varies with changes in pressure in the wellbore.